Primer for battery electrode

ABSTRACT

Primer arrangements that facilitate electrical conduction and adhesive connection between an electroactive material and a current collector are presented. In some embodiments, primer arrangements described herein include first and second primer layers. The first primer layer may be designed to provide good adhesion to a conductive support. In one particular embodiment, the first primer layer comprises a substantially uncrosslinked polymer having hydroxyl functional groups, e.g., polyvinyl alcohol. The materials used to form the second primer layer may be chosen such that the second primer layer adheres well to both the first primer layer and an electroactive layer. In certain embodiments including combinations of first and second primer layers, one or both of the first and second primer layers comprises less than 30% by weight of a crosslinked polymeric material. A primer including only a single layer of polymeric material is also provided.

RELATED APPLICATIONS

This application is continuation of U.S. application Ser. No.12/682,011, filed Jul. 30, 2010, which is a U.S. National Stage patentapplication based on International Application No. PCT/US2008/12042,filed Oct. 23, 2008, which claims priority to U.S. ProvisionalApplication No. 61/000,582, filed Oct. 26, 2007 and U.S. ProvisionalApplication No. 61/035,845, filed Mar. 12, 2008, each of which areincorporated herein by reference in their entirety.

FIELD OF INVENTION

The present invention relates generally to electrochemical cells, andmore specifically, to primers for electrodes of electrochemical cells.

BACKGROUND

A typical electrochemical cell has a cathode and an anode whichparticipate in an electrochemical reaction. To fabricate an electrode,electroactive materials can be deposited onto a conductive support,which can act as a current collector for the electrode. Maintainingelectrical contact between the electroactive material and the conductivesupport is vital to efficient functioning of the electrochemical cell.

It is known that adhesion layers, also known as “primers” or “primerlayers”, deposited between the electroactive material and the conductivesupport can adhere to and provide electrical communication between theelectroactive material and conductive support. Although existing primersare available, many do not provide good adhesion to both theelectroactive material and conductive support simultaneously, while alsoproviding good electrical contact between the layers. As a result, someelectrochemical cells including such primers have low dischargecapacities. Accordingly, there is a need for primers that 1) providegood adhesion and electrical contact between the electroactive materialand conductive support to promote high discharge capacities in anelectrochemical cell, 2) are compatible with the electrolyte, and 3) areable to protect the current collector from possible corrosive effects ofelectroactive species in the electrochemical cell during charge and/ordischarge.

SUMMARY OF THE INVENTION

Electrochemical cells, and more specifically, primers for electrodes ofelectrochemical cells are provided.

In one embodiment, an electrode is provided. The electrode comprises aconductive support, a first primer layer positioned adjacent theconductive support and comprising a first polymeric material, whereinthe first primer layer comprises less than 30% by weight of acrosslinked polymeric material. The electrode also includes a secondprimer layer positioned adjacent the first primer layer and comprising asecond polymeric material, wherein the second primer layer comprisesless than 30% by weight of a crosslinked polymeric material. Theelectrode also includes an electroactive layer in electricalcommunication with the second primer layer.

In another embodiment, a current collector is provided. The currentcollector comprises a conductive support, a first primer layerpositioned adjacent the conductive support and comprising a firstpolymeric material, and a second primer layer positioned adjacent thefirst primer layer and comprising a second polymeric material, whereinthe first and/or second polymeric materials comprises hydroxylfunctional groups.

In another embodiment, an electrode comprises a conductive support and afirst primer layer positioned adjacent the conductive support andcomprising a first polymeric material, wherein the first primer layercomprises greater than 30% by weight of a crosslinked polymericmaterial. The electrode also includes a second primer layer positionedadjacent the first primer layer and comprising a second polymericmaterial, wherein the second primer layer comprises greater than 30% byweight of a crosslinked polymeric material. The electrode also includesan electroactive layer in electrical communication with the secondprimer layer.

In another embodiment, a method of forming a cathode is provided. Themethod comprises positioning at least one primer layer adjacent aconductive support, the primer layer comprising a polymeric materialthat includes hydroxyl functional groups. Optionally, at least a portionof the polymeric material may be crosslinked. The method also includespositioning a cathode slurry adjacent the primer layer, the cathodeslurry comprising a cathode active material, a conductive filler, and asolvent, wherein the cathode slurry comprises greater than 30% by weightof water. At least a portion of the solvent can be removed from thecathode slurry.

In another embodiment, a cathode is provided. The cathode comprises aconductive support, and a primer layer positioned adjacent theconductive support and comprising a polymeric material that includeshydroxyl functional groups. Optionally, at least a portion of thepolymeric material may be crosslinked. The cathode also includes acathode active layer in electrical communication with the primer layer,wherein the cathode active layer is made by a process in which itcomprises greater than 30% by weight of water prior to being dried.

In another embodiment, a method of forming a cathode is provided. Themethod comprises mixing a polymeric material comprising hydroxylfunctional groups in a solvent at a temperature of greater than 80° C.,adding a conductive filler to the polymeric material and solvent to forma primer slurry, and positioning the primer slurry on a conductivesupport to form a primer layer. The method also includes positioning acathode slurry adjacent the primer layer, the cathode slurry comprisinga cathode active material, a conductive filler, and a solvent. At leasta portion of the solvent may be removed from the cathode slurry.

In another embodiment, a lithium battery is provided. The lithiumbattery comprises an anode comprising lithium metal as the active anodespecies and a cathode comprising sulfur as the active cathode speciessupported by a cathode current collector. The area specific resistanceof the lithium battery is less than 50 ohm·cm². In certain embodiments,the area specific resistance is less than 40, 30, 20, or 10 ohm·cm². Thelithium battery may further include a primer layer positioned betweenthe active cathode species and the cathode current collector. In oneembodiment, the primer layer comprises a polymeric material comprisinghydroxyl groups. For instance, the primer layer may comprise or beformed of polyvinyl alcohol, which may be at least partially crosslinkedor substantially uncrosslinked.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 shows an electrode including first and second primer layers, anelectroactive layer, and a conductive support according to oneembodiment of the invention;

FIG. 2 shows a primer including first and second primer layers and anintermediate layer attached to a conductive support according to anotherembodiment of the invention;

FIG. 3 shows a single-layer primer attached to a conductive supportaccording to another embodiment of the invention;

FIG. 4 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Example 1 and Comparative Example1 according to another embodiment of the invention;

FIG. 5 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Example 2, and ComparativeExample 2 according to another embodiment of the invention;

FIG. 6 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Example 4 and Comparative Example3 according to another embodiment of the invention;

FIG. 7 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Examples 4, 5, 6, and ComparativeExample 4 according to another embodiment of the invention;

FIG. 8 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Example 7 and Comparative Example5 according to another embodiment of the invention;

FIG. 9 shows specific discharge capacity as a function of cell cycle forthe electrochemical cells described in Example 8 and Comparative Example6 according to another embodiment of the invention, and

FIG. 10 shows polarization as a function of discharge current for theelectrochemical cells described in Example 10 and Comparative Example 8according to another embodiment of the invention.

DETAILED DESCRIPTION

The present invention relates generally to electrochemical cells, andmore specifically, to primers for electrodes of electrochemical cells.In particular, primer arrangements and compositions that facilitateelectrical conduction and adhesive connection between an electroactivelayer and a current collector are presented. In some embodiments, primerarrangements described herein include first and second primer layers,which can be of the same or different material. The first primer layermay be designed to provide good adhesion to a conductive support and maycomprise, for example, a crosslinked or substantially uncrosslinkedpolymer (e.g., a binder) having hydroxyl functional groups, e.g.,polyvinyl alcohol. The materials used to form the second primer layermay be chosen such that the second primer layer adheres well to both thefirst primer layer and an electroactive layer. In certain embodimentsincluding combinations of first and second primer layers, one or both ofthe first and second primer layers comprises less than 30% by weight ofa crosslinked polymeric material. In other embodiments, one or both ofthe first and second primer layers comprises between 30-60% by weight ofa crosslinked polymeric material. A primer including only a single layerof polymeric material is also provided.

One aspect of the invention is the discovery that low degrees ofcrosslinking, or essentially no crosslinking, in one or more primerlayers for devices as described herein function well. Those of ordinaryskill in the art would have expected that as crosslinking of a primerlayer is reduced or eliminated, cohesion of that primer layer underrelatively rigorous conditions to which the device is subjected inpractice might be compromised to the extent that the device would failprematurely; crosslinking would be expected to improve cohesion of aprimer layer to increase robustness. It would have been unexpected thatimproved adhesion properties between primer layers (and/or between aprimer layer and a conductive support or an electroactive material),facilitated by little or no crosslinking within the primer layers, wouldbe possible while still maintaining intra primer layer cohesionnecessary for sufficient robustness. Certain aspects of the presentinvention therefore are surprising in the combination of reduced oressentially eliminated crosslinking of one or more primer layers withboth sufficient adhesion and internal cohesion within and between primerlayers for a robust device. The working examples and appended figuresdemonstrate this robustness.

Accordingly, in certain embodiments, the primer layers described hereinare constructed and arranged to have one or more of the followingfeatures: good adhesion and electrical conduction between the currentcollector and the primer layer (e.g., a first primer layer), goodadhesion and electrical conduction between the first primer layer and asecond primer layer in a multi-layer primer, good adhesion andelectrical conduction between the primer layer (e.g., a second primerlayer) and an electroactive layer (which may comprise electroactivematerials and other optional additives such as electronically conductivematerials), and prevention of possible corrosive effects of theelectroactive material on the current collector, e.g., during chargeand/or discharge. Additionally, batteries described herein comprisingprimers of the invention may have lower area specific resistance thanbatteries including certain commercial primers.

Primer layer(s) described herein are preferably thin (e.g., less thanabout 10 microns) to reduce overall battery weight. Furthermore, primerlayer(s) should be stable in the electrolyte and should not interferewith the structural integrity of the electrodes in order for theelectrochemical cell to have a high electrochemical “capacity” or energystorage capability (i.e., reduced capacity fade).

Many embodiments described herein involve lithium-sulfur rechargeablebatteries (i.e., batteries including a sulfur-containing cathode and alithium anode). However, wherever lithium-sulfur batteries aredescribed, it is to be understood that any analogous alkali metalbattery (alkali metal anode) can be used, and wherever cathodesincluding sulfur as an active cathode species are described herein, itis to be understood that any suitable cathode active species can beused. Additionally, although rechargeable batteries are intended tobenefit from the invention, non-rechargeable (i.e., primary) batteriesare intended to benefit from the invention as well. Furthermore,although embodiments of the invention are particularly useful foradhering an electrochemically active layer to an electrically conductivematerial with different structural and surface properties, the presentinvention may be applicable to other applications in which adhesionand/or electrical connection is desired.

As described above, one aspect of the invention involves a multi-layerprimer that achieves good adhesion to both a conductive support and anelectroactive material. As shown in the illustrative embodiment of FIG.1, electrode 2 includes conductive support 22 and primer 4. Primer 4includes a first primer layer 24 adjacent the conductive support, aswell as second primer layer 26 adjacent the first primer layer. Asshown, second primer layer 26 is in electrical communication withelectroactive layer 30 (e.g., a cathode active layer comprising sulfuror an anode active layer comprising lithium metal). Optionally,additional layers (not shown), such as a multi-layer structure thatprotects the electroactive material from the electrolyte, may be presenton top of electroactive material 30, as described in more detail in U.S.patent application Ser. No. 11/400,781, filed Apr. 6, 2006, entitled,“Rechargeable Lithium/Water, Lithium/Air Batteries” to Affinito et al.,which is incorporated herein by reference in its entirety.

In some embodiments, one or both of first primer layer 24 and secondprimer layer 26 are formed of a polymeric material. The polymericmaterials used to form the two layers may be the same or different. Insome cases, at least a portion of the polymeric material of the firstand/or second primer layers is/are crosslinked; in other cases, thepolymeric material(s) is/are substantially uncrosslinked.

At least a portion of a polymer is crosslinked when there arecrosslinking bonds connecting two or more individual polymer chains toone another at at least one position not at a terminal end of one of thepolymer chains. For instance, in cases in which a primer layer comprisesa certain percentage by weight of a crosslinked polymeric material, thatpercentage by weight of the individual polymer chains within that layermay be linked at at least one intermediate (e.g., non-terminal) positionalong the polymer chain with another polymer chain within that layer. Insome embodiments, crosslinking bonds are covalent bonds. In otherembodiments, crosslinking bonds are ionic bonds. Together, crosslinkedpolymer chains create interconnected, three-dimensional polymernetworks. Crosslinking bonds attaching independent polymer chains to oneanother may be generated by methods such as UV radiation,gamma-radiation, crosslinking agents, thermal stimulation, photochemicalstimulation, electron beams, self-crosslinking, free radicals, and othermethods known to one of ordinary skill in the art.

In some cases, the first and/or second primer layer comprises less than30% by weight of a crosslinked polymeric material (e.g., as determinedafter the primer layer has been dried). That is, less than 30% by weightof the individual polymer chains which form the polymeric material of aparticular layer may be crosslinked at at least one intermediate (e.g.,non-terminal) position along the chain with another individual polymerchain within that layer. One or both of the first and second primerlayers may comprise less than 25% by weight, less than 20% by weight,less than 15% by weight, less than 10% by weight, less than 5% byweight, or less than 2% by weight, or 0% of a crosslinked polymericmaterial. In certain embodiments, the first and/or second primer layercomprises less than 30% by weight of a covalently crosslinked polymericmaterial. For example, one or both of the first and second primer layersmay comprise less than 25% by weight, less than 20% by weight, less than15% by weight, less than 10% by weight, less than 5% by weight, or lessthan 2% by weight, or 0% of a covalently crosslinked polymeric material.In one particular embodiment, one or both of the first and second primerlayers is essentially free of covalently crosslinked material.

It should be understood that while a primer layer may include, forexample, less than 30% by weight of a crosslinked polymeric material,the total amount of polymeric material (e.g., combined crosslinked andnon-crosslinked polymeric material) in the primer layer may vary, e.g.,from 20-90% by weight of the primer layer, as described in more detailbelow.

In one particular embodiment, first primer layer 24 comprises less than30% by weight of a crosslinked polymeric material (e.g., polyvinylalcohol) and second primer layer 26 also includes less than 30% byweight of a crosslinked polymeric material (e.g., polyacrylate,polyvinyl pyrrolidone vinyl acetate copolymer, and polyvinyl butyral).In other embodiments, a one of the first and second primer layerscomprises less than 30% by weight of a crosslinked polymeric material,and the other of the first and second primer layers comprises greaterthan 30% by weight of a crosslinked polymeric material. In yet otherembodiments, both of the first and second primer layers may includegreater than 30% by weight of a crosslinked polymeric material.

Sometimes, an electrode includes first and second primer layers that areformed of the same material, but the first and second primer layers havedifferent degrees of crosslinking. For instance, the first primer layermay comprise substantially uncrosslinked polyvinyl alcohol, and thesecond primer layer may comprise crosslinked polyvinyl alcohol. Otherarrangements are also possible.

In some embodiments, the one or more primer layers of a primer comprisea substantially uncrosslinked polymeric material. As used herein, theterm “substantially uncrosslinked” means that during normal processingof the polymeric material to form a primer layer and to fabricate anelectrochemical cell associated therewith, methods commonly known forinducing crosslinking in the polymeric material, such as exposure toultraviolet (UV) radiation and addition of crosslinking agents, are notused. A substantially uncrosslinked material may be essentially free ofcrosslinked material to the extent that it has no greater degree ofcrosslinking than is inherent to the polymeric material. In someembodiments, a substantially uncrosslinked material is essentially freeof crosslinked material to the extent that it has no greater degree ofcrosslinking than is inherent to the polymeric material after normalprocessing of the polymeric material to form the primer layer and tofabricate an electrochemical cell associated therewith. Typically, asubstantially uncrosslinked material has less than 10% by weight, lessthan 7% by weight, less than 5% by weight, less than 2% by weight, orless than 1% by weight of crosslinked polymeric material in itscomposition. In certain embodiments, a substantially uncrosslinkedmaterial has less than 10% by weight, less than 7% by weight, less than5% by weight, less than 2% by weight, or less than 1% by weight ofcovalently crosslinked polymeric material in its composition.

In one embodiment, first primer layer 24 of FIG. 1 comprises less than30% by weight of a crosslinked polymeric material (e.g., less than 20%,less than 15%, or less than 10% of a crosslinked polymeric material) andsecond primer layer 26 is substantially crosslinked to varying degrees.The first primer layer may be substantially uncrosslinked orcrosslinked, for example, to less than 30% by weight, to allow it tohave adequate adhesion to the second primer layer. The second primerlayer may comprise, for example, greater than 10% by weight, greaterthan 20% by weight, greater than 30% by weight, greater than 40% byweight, greater than 50% by weight, greater than 60% by weight, greaterthan 70% by weight, greater than 80% by weight, or greater than 90% byweight of a crosslinked polymeric material. One or more of the methodsdescribed above that induce crosslinking such as exposure of thematerial to UV radiation or to a crosslinking agent may be used.Crosslinking of the second primer layer may, in some cases, promotebetter adhesion of the second primer layer with one or both of theelectroactive layer and first primer layer. As described in more detailbelow, the formation of an electrode including a crosslinked secondprimer layer may optionally involve the addition of a component (e.g., asolvent) in the electroactive layer that preferentially interacts with acomponent in the second primer layer. The second primer layer may becrosslinked to the electroactive layer and/or first primer layer, orsubstantially uncrosslinked to the electroactive layer and/or firstprimer layer.

In another embodiment, at least a portion of a polymeric material of thefirst primer layer is crosslinked and the polymeric material of thesecond primer layer is optionally crosslinked or substantiallyuncrosslinked. The first primer layer (and, optionally, the secondprimer layer) may comprise, for example, greater than 10% by weight,greater than 20% by weight, greater than 30% by weight, greater than 40%by weight, greater than 50% by weight, greater than 60% by weight,greater than 70% by weight, greater than 80% by weight, or greater than90% by weight of a crosslinked polymeric material. Other arrangements ofcrosslinked or substantially uncrosslinked first and second primerlayers are also possible.

Polymeric material may be crosslinked to varying degrees depending onthe number of chains involved in at least one crosslinking bond. Thepercent by weight of crosslinked polymer out of a total mass ofpolymeric material may be determined by identifying the mass of polymersengaged in crosslinking bonds relative to the whole mass underconsideration. Such a determination may be achieved by one of ordinaryskill in the art by a variety of scientific methods including, forexample, FTIR and differential scanning calorimetry (DCS).

Another multi-layer primer arrangement is illustrated in FIG. 2. Asshown in the illustrative embodiment of FIG. 2, electrode 5 comprisescurrent collector 6 including primer 8. Primer 8 comprises first primerlayer 24 separated from second primer layer 26 by intermediate layer 28.Electroactive material 30 is in electrical communication with the secondprimer layer. In some embodiments, intermediate layer 28 is a thirdprimer layer. Accordingly, in some embodiments of the invention, primersincluding more than two primer layers may be used as appropriate. Inother embodiments, intermediate layer 28 is a conductive supportmaterial, a metal layer, a plasma treated layer, an ionic layer, or thelike. The composition and thickness of layer 28 may be chosen, forexample, based on its electrical conductivity, adhesiveness, and/orother mechanical or physical properties. In other embodiments,intermediate layer 28 is positioned between the electroactive material30 and second primer layer 26, and/or between first primer layer 24 andconductive support 22. In some cases, an electrode of the inventionincludes two or more intermediate layers positioned between variouslayers of the electrode.

As illustrated in FIG. 2, first primer layer 24 is adjacent secondprimer layer 26 via a third, intermediate layer 28. In otherembodiments, e.g., as shown in FIG. 1, first primer layer 24 isimmediately adjacent second primer layer 26.

Another aspect of the invention is the unexpected discovery that asingle-layer primer positioned between a conductive support and anelectroactive material layer can provide good adhesion and electricalcommunication between such layers. Typically in some batteries of thistype, a single-layer primer can provide good adhesion and electricalcommunication to one, but not both, of the conductive support andelectroactive material. For instance, a single-layer primer formed of asubstantially non-crosslinked material may, in some cases, have goodadhesion to the electroactive material, but poor adhesion to theconductive support. On the other hand, certain single-layer primersformed of a crosslinked polymeric material may have good adhesion to theconductive support, but poor adhesion to the electroactive material. Theinventors have discovered, however, that by processing the single-layerprimer and electroactive material layer in a particular manner thatpromotes physical and/or chemical interaction between the appropriatelayers, good adhesion of the single-layer primer to both the conductivesupport and electroactive material can be achieved.

An example of an electrode including a single-layer primer positionedbetween a current collector and an electroactive material is shown inFIG. 3. As shown in the embodiment illustrated in FIG. 3, electrode 10includes conductive support 22 in electrical communication withelectroactive material 30 via primer layer 24. The single-layer primermay be crosslinked in some embodiments, but uncrosslinked in others.Advantageously, a single-layer primer that can provide good electricalconnection as well as good adhesion to both the conductive support andthe electroactive material can reduce the overall battery weight, aswell as the number of fabrication steps required to assemble thebattery. It should be understood that in some embodiments, electrode 10can include other components such as an intermediate layer (e.g., aplasma treated layer) between layers 22 and 24 and/or between layers 24and 30; such an intermediate layer may improve adhesion between theadjacent layers.

The inventors have unexpectedly discovered that certain primer layer(s)can provide good adhesion between the conductive support, theelectroactive material, and/or a second primer layer, e.g., by modifyingthe composition of one or more of the layers during processing. In oneembodiment, this is achieved by including components in both the primerlayer and electroactive material layer that interact favorably with eachother to promote adhesion. For example, in one embodiment, the primerlayer includes hydroxyl functional groups and the electroactive materialis formed as a slurry (i.e., a mixture of at least two components)including a relatively high amount of water (e.g., 20-80 wt % water).Additionally or alternatively, in certain embodiments a relatively highamount of water may be present in a slurry of the primer composition.Without wishing to be bound by theory, the inventors hypothesize thatthe water in the slurry can solubilize at least portions of a polymerwithin the slurry. For instance, the water may solubilize all orportions of the polymeric material (e.g., polyvinyl alcohol) used toform the primer layer (or electroactive layer). The solubilized polymercan then participate in hydrogen bonding with hydroxyl surface groupsthat may be present at a surface in contact with the polymer, which cancause good adhesion between the polymer and the surface. For example, ifthe electroactive layer includes a material that can hydrogen bond withthe hydroxyl groups of the primer layer, better adhesion may beachieved. In another example, a surface in contact with the primer layermay be an aluminum current collector that includes a surface layer ofaluminum oxide; a portion of the surface layer may also include hydroxylgroups. These hydroxyl surface groups can participate in hydrogenbonding with the hydroxyl groups of the solvated polymer of the primerlayer. In addition, in some embodiments, the solubilized polymer of afirst primer layer may physically interact with a polymeric material(e.g., of a second primer layer or an electroactive material layer) incontact with the first primer layer such that the molecules (e.g.,polymer chains) of each layer are entangled with one another at theinterface. This entanglement can lead to adhesion of the two layers evenafter drying of the layers (when water and/or other solvents may beremoved).

Additionally or alternatively, the electroactive material layer mayinclude certain chemical compositions that interact favorably with theprimer layer and which remain in the electroactive material layer evenafter drying. For example, the electroactive material layer may includea polymeric material (e.g., a binder) or other material containingcertain functional groups (e.g., hydroxyl or ether groups) that caninteract with those of the primer layer. In one particular embodiment,both the electroactive material layer and the primer layer include oneor more polymers that can crosslink with each other. The primer layermay be prepared such that it has a relatively high amount (e.g., anexcess) of crosslinking agent. Upon positioning of the slurry containingthe electroactive material adjacent the primer layer, crosslinking agentat the interface of the two layers can cause crosslinking between apolymer in the electroactive material layer and a polymer in the primerlayer.

According to one embodiment of the invention, a method of forming anelectrode (e.g., a cathode) includes positioning a primer layercomprising a polymeric material including hydroxyl functional groups, atleast a portion of the polymeric material being crosslinked, adjacent aconductive support. An electrode slurry can be positioned adjacent theprimer layer, the electrode slurry comprising greater than 10 wt %,greater than 20 wt %, greater than 30 wt %, or greater than 40 wt % of asolvent (e.g., water) that can interact with a component in the primerlayer (e.g., a hydroxyl-containing polymer such as polyvinyl alcohol).In some instances, the electrode slurry includes between 30-60 wt % ofsuch a solvent (e.g., water). The electrode may then be partially orcompletely dried to remove at least a portion of the solvent. Thisprocess can result in good adhesion between the layers.

In other embodiments, the electrode slurry can include other solvents inaddition to, or in place of, water (e.g., other solvents that can form ahydrogen bond), which can result in favorable interactions withcomponents of the primer layer. In these and other embodiments, theprimer layer may also be processed in a manner that allows it tointeract favorably with components of the electroactive material layer.For example, to promote dissolution and/or dispersion of the polymericmaterial of the primer layer, the polymeric material may be mixed in anappropriate solvent at a temperature of greater than 60° C., greaterthan 70° C., greater than 80° C., or greater than 90° C. prior topositioning the primer layer.

It should be understood that the compositions and methods describedabove may be used to achieve good adhesion for single-layer primers,multi-layer primers, and other applications in which good adhesionand/or electrical connection is desired.

As described above, in some embodiments, a primer layer described herein(e.g., the first and/or second polymeric materials of the first and/orsecond primer layers, respectively, of FIGS. 1-2 and/or the primer layerof FIG. 3) comprises hydroxyl functional groups. Hydroxyl groups mayprovide good adhesion to a conductive support such as an aluminum foiland/or an aluminized polyethylene terephthalate (PET) film. Non-limitingexamples of hydroxyl-containing polymers include polyvinyl alcohol,polyvinyl butyral, polyvinyl formal, vinyl acetate-vinyl alcoholcopolymers, ethylene-vinyl alcohol copolymers, and vinyl alcohol-methylmethacrylate copolymers. The hydroxyl-containing polymer may havevarying levels of hydrolysis (thereby including varying amounts ofhydroxyl groups). For instance, a vinyl-based polymer may be greaterthan 50% hydrolyzed, greater than 60% hydrolyzed, greater than 70%hydrolyzed, greater than 80% hydrolyzed, greater than 90% hydrolyzed,greater than 95% hydrolyzed, or greater than 99% hydrolyzed. A greaterdegree of hydrolysis may allow better adhesion of thehydroxyl-containing material to a conductive support and, in some cases,may cause the polymer to be less soluble in the electrolyte. In otherembodiments, a polymer having hydroxyl groups may be less than 50%hydrolyzed, less than 40% hydrolyzed, less than 30% hydrolyzed, lessthan 20% hydrolyzed, or less than 10% hydrolyzed with hydroxylfunctional groups. In one particular embodiment, a first primer layercomprises hydroxyl groups and a second primer layer has a differentmaterial composition than that of the first primer layer.

In some embodiments, a primer layer described herein comprises polyvinylalcohol. The polyvinyl alcohol in a primer layer may be crosslinked insome instances, and substantially uncrosslinked in other instances. Inone particular embodiment, a primer layer immediately adjacent aconductive support (e.g., a first primer layer) comprises polyvinylalcohol. In another embodiment, the primer layer consists essentially ofpolyvinyl alcohol. The polyvinyl alcohol in such embodiments may besubstantially uncrosslinked, or in other cases, less than 30% of thematerial used to form the first primer layer is crosslinked. Forinstance, a primer layer immediately adjacent a conductive support andincluding polyvinyl alcohol may comprise less than 30% by weight, lessthan 20% by weight, less than 15% by weight, less than 10% by weight,less than 5% by weight, or less than 2% by weight, of crosslinkedpolyvinyl alcohol. Such a primer layer may optionally be adjacent asecond primer layer, which may have a different material compositionthan that of the first primer layer. In some instances, the secondprimer layer is crosslinked. The second primer layer may comprise anysuitable material that can adhere well to the first primer layer and theelectroactive material. Examples of such materials include, but are notlimited to, polyvinyl butyral, polyacrylate, polyvinyl pyrrolidone, andpolyvinyl acetate, as well as copolymers thereof. Other suitablepolymers are described in more detail below. In one particularembodiment, the material used to form the second primer layer iscrosslinked so as to provide good adhesion between the first primerlayer and a sulfur-containing cathodes.

In certain embodiments, two primer layers of a primer comprise polymershaving hydroxyl functional groups. The percentage of hydroxyl functionalgroups in the polymers of the first and second primer layers may differ.For example, in one embodiment, the first primer layer comprises atleast at least 20% more, at least 40% more, at least 60% more, at least80% more, at least 100% more, at least 150% more, or at least 200% morehydroxyl groups than the second primer layer. One particular example isa first primer layer comprising polyvinyl alcohol and a second primerlayer comprising polyvinyl butyral (e.g., where polyvinyl alcohol hasbeen reacted to varying degrees with butanal and/or other compounds).

A crosslinking agent is a molecule with a reactive portion(s) designedto interact with functional groups on the polymer chains in a mannerthat will form a crosslinking bond between one or more polymer chains.Examples of crosslinking agents that can crosslink polymeric materialsused for primer layers described herein include, but are not limited to:polyamide-epichlorohydrin (polycup 172); aldehydes (e.g., formaldehydeand urea-formaldehyde); dialdehydes (e.g., glyoxal, glutaraldehyde, andhydroxyadipaldehyde); acrylates (e.g., ethylene glycol diacrylate,di(ethylene glycol) diacrylate, tetra(ethylene glycol) diacrylate,methacrylates, ethylene glycol dimethacrylate, di(ethylene glycol)dimethacrylate, tri(ethylene glycol) dimethacrylate); amides (e.g.,N,N′-methylenebisacrylamide, N,N′-(1,2-dihydroxyethylene)bisacrylamide,N-(1-hydroxy-2,2-dimethoxyethyl)acrylamide); silanes (e.g.,methyltrimethoxysilane, methyltriethoxysilane, tetramethoxysilane(TMOS), tetraethosxysilane (TEOS), tetrapropoxysilane,methyltris(methylethyldetoxime)silane, methyltris(acetoxime)silane,methyltris(methylisobutylketoxime)silane,dimethyldi(methylethyldetoxime)silane,trimethyl(methylethylketoxime)silane,vinyltris(methylethylketoxime)silane,methylvinyldi(mtheylethylketoxime)silane,methylvinyldi(cyclohexaneoneoxxime)silane,vinyltris(mtehylisobutylketoxime)silane, methyltriacetoxysilane,tetraacetoxysilane, and phenyltris(methylethylketoxime)silane);divinylbenzene; melamine; zirconium ammonium carbonate;dicyclohexylcarbodiimide/dimethylaminopyridine (DCC/DMAP);2-chloropyridinium ion; 1-hydroxycyclohexylphenyl ketone; acetophenondimethylketal; benzoylmethyl ether; aryl trifluorovinyl ethers;benzocyclobutenes; phenolic resins (e.g., condensates of phenol withformaldehyde and lower alcohols, such as methanol, ethanol, butanol, andisobutanol), epoxides; melamine resins (e.g., condensates of melaminewith formaldehyde and lower alcohols, such as methanol, ethanol,butanol, and isobutanol); polyisocyanates; dialdehydes; and othercrosslinking agents known to those of ordinary skill in the art.

In embodiments including a crosslinked polymeric material and acrosslinking agent, the weight ratio of the polymeric material to thecrosslinking agent may vary over a wide range for reasons including thefunctional-group content of the polymer, its molecular weight, thereactivity and functionality of the crosslinking agent, the desired rateof crosslinking, the degree of stiffness/hardness desired in thepolymeric material, and the temperature at which the crosslinkingreaction may occur. Non-limiting examples of ranges of weight ratiosbetween the polymeric material and the crosslinking agent include from100:1 to 50:1, from 20:1 to 1:1, from 10:1 to 2:1, and from 8:1 to 4:1.

As mentioned above, a primer layer may include any suitable amount ofpolymeric material to achieve the desired properties. For example, thetotal amount of polymeric material (e.g., combined crosslinked andnon-crosslinked polymeric material) in a primer layer may be in therange of, for example, 20-90% by weight of the primer layer (e.g., asdetermined after drying the primer layer). In some instances, a primerlayer includes a total amount of a polymeric material in the range of,for example, 20-40%, 30-60%, 40-80%, or 60-80% by weight of the primerlayer. The remaining material used to form the primer layer may includea conductive filler, a crosslinking agent, and/or other materials asdescribed herein.

Certain types of polymers are known to form crosslinking bonds underappropriate conditions. Non-limiting examples of crosslinkable polymersinclude: polyvinyl alcohol, polyvinylbutryl, polyvinylpyridyl, polyvinylpyrrolidone, polyvinyl acetate, acrylonitrile butadiene styrene (ABS),ethylene-propylene rubbers (EPDM), EPR, chlorinated polyethylene (CPE),ethelynebisacrylamide (EBA), acrylates (e.g., alkyl acrylates, glycolacrylates, polyglycol acrylates, ethylene ethyl acrylate (EEA)),hydrogenated nitrile butadiene rubber (HNBR), natural rubber, nitrilebutadiene rubber (NBR), certain fluoropolymers, silicone rubber,polyisoprene, ethylene vinyl acetate (EVA), chlorosulfonyl rubber,flourinated poly(arylene ether) (FPAE), polyether ketones, polysulfones,polyether imides, diepoxides, diisocyanates, diisothiocyanates,formaldehyde resins, amino resins, plyurethanes, unsaturated polyethers,polyglycol vinyl ethers, polyglycol divinyl ethers, copolymers thereof,and those described in U.S. Pat. No. 6,183,901 to Ying et al. of thecommon assignee for protective coating layers for separator layers.Those of ordinary skill in the art can choose appropriate polymers thatcan be crosslinked, as well as suitable methods of crosslinking, basedupon general knowledge of the art in combination with the descriptionherein.

Other classes polymers that may be suitable for use in a primer layer(either crosslinked or non-crosslinked) include, but are not limited to,polyamines (e.g., poly(ethylene imine) and polypropylene imine (PPI));polyamides (e.g., polyamide (Nylon), poly(ε-caprolactam) (Nylon 6),poly(hexamethylene adipamide) (Nylon 66)), polyimides (e.g., polyimide,polynitrile, and poly(pyromellitimide-1,4-diphenyl ether) (Kapton));vinyl polymers (e.g., polyacrylamide, poly(2-vinyl pyridine),poly(N-vinylpyrrolidone), poly(methylcyanoacrylate),poly(ethylcyanoacrylate), poly(butylcyanoacrylate),poly(isobutylcyanoacrylate), poly(vinyl acetate), poly (vinyl alcohol),poly(vinyl chloride), poly(vinyl fluoride), polyvinylidene fluorides(PVF₂ or PVDF), poly(2-vinyl pyridine), polychlorotrifluoro ethylene,poly(isohexylcynaoacrylate), polyisobutylene, poly(methyl styrene),poly(methylmethacrylate) (PMMA), polyethylacrylate,polyethylmethacrylate, UV curable acrylates or methacrylates);polyacetals; polyolefins (e.g., poly(butene-1), poly(n-pentene-2),polypropylene, polytetrafluoroethylene (Teflon)); polyesters (e.g.,polycarbonate, polybutylene terephthalate, polyhydroxybutyrate);polyethers (poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO),poly(tetramethylene oxide) (PTMO), heat curable divinyl ethers);polyaramides (e.g., poly(imino-1,3-phenylene iminoisophthaloyl) andpoly(imino-1,4-phenylene iminoterephthaloyl)); polyheteroaromaticcompounds (e.g., polybenzimidazole (PBI), polybenzobisoxazole (PBO) andpolybenzobisthiazole (PBT)); polyheterocyclic compounds (e.g.,polypyrrole); polyurethanes; phenolic polymers (e.g.,phenol-formaldehyde); polyalkynes (e.g., polyacetylene); polydienes(e.g., 1,2-polybutadiene, cis or trans-1,4-polybutadiene,ethylene-propylene-diene (EPDM) rubbers); polysiloxanes (e.g.,poly(dimethylsiloxane) (PDMS), poly(diethylsiloxane) (PDES),polydiphenylsiloxane (PDPS), and polymethylphenylsiloxane (PMPS)); andinorganic polymers (e.g., polyphosphazene, polyphosphonate, polysilanes,polysilazanes). The mechanical and physical properties (e.g.,conductivity, resistivity) of these polymers are known. Accordingly,those of ordinary skill in the art can choose suitable polymers for usein lithium batteries, e.g., based on their mechanical and/or electronicproperties, adhesiveness to conductive supports and/or electroactivematerials, solubility in a particular electrolyte, etc., by, forexample, tailoring the amounts of components of polymer blends,adjusting the degree of cross-linking (if any), etc. Simple screeningtests such as those described herein can be used to select polymers thathave the physical/mechanical properties.

The above examples of crosslinkable polymers may be crosslinked, orsubstantially uncrosslinked, in primer layers of the invention. Inaddition, other types of polymers may be used as first and/or secondprimer layers of the invention. The above examples of polymers may alsobe used in electroactive material layers described herein.

Determining suitable compositions, configurations (e.g., crosslinked orsubstantially uncrosslinked) and dimensions of primers can be carriedout by those of ordinary skill in the art, without undueexperimentation. As described above in connection with a multi-layerprimer, a first primer layer may be chosen based on, for example, itselectrically conductive properties, its inertness in the electrolyte,and its ability to adhere to the current collector and, optionally, to asecond primer layer. A suitable second primer layer may provide goodadhesion between the electroactive material (and/or other additives,e.g., an electronically conductive material, of an electroactive layer)and the first primer layer, while having good electrical conductivityand inertness in the electrolyte. The particular materials used to formthe first and/or second primer layers may depend on, for example, thematerial compositions of the conductive support, electroactive material,and electrolyte, as well as the method used to deposit the layers. Thedimensions of the primer layers may be chosen such that theelectrochemical cell has a low overall weight, while providing suitableadhesion to their respective adjacent layers.

One simple screening test for choosing appropriate materials for aprimer layer may include forming the primer layer and immersing thelayer in an electrolyte and observing whether inhibitory or otherdestructive behavior (e.g., delamination) occurs compared to that in acontrol system. The same can be done with other layers (e.g., one ormore of the conductive support, electroactive material, and/or otherprimer layer) attached to the primer layer. Another simple screeningtest may include forming an electrode including the one or more primerlayers and immersing the electrode in the electrolyte of the battery inthe presence of the other battery components, discharging/charging thebattery, and observing whether specific discharge capacity is higher orlower compared to a control system. A high discharge capacity mayindicate good adhesion and/or electrical conduction between therespective components of the battery, and a low discharge capacity mayindicate delamination, poor electrical conductivity in a layer, and/orpoor electrical communication between layers of the electrode. To testwhether a primer layer adheres adequately, a wipe test may be performed.The wipe test may include, for example, applying a solvent (e.g.,isopropyl alcohol) to the primer layer and determining whether theprimer layer can be wiped away with the solvent. Adhesion can also betested by bending the layers to determine whether delamination occursbetween the layers. Another simple screening test may include measuringthe adhesiveness or force required to remove a primer layer from a unitarea of a surface (e.g., a peel test), which can be measured in N/m²,using a tensile testing apparatus or another suitable apparatus. Suchexperiments can optionally be performed in the presence of a solvent(e.g., an electrolyte) or other components (e.g., fillers) to determinethe influence of the solvent and/or components on adhesion. Anotherpossible screening is a scotch tape test where a strip of tape isapplied on the primer layer and removed. If primer stays on theconductive layer, adhesion is good. If the primer layer comes off withthe strip of tape, adhesion is poor. Other simple tests are known andcan be conducted by those of ordinary skill in the art.

The thickness of a primer layer (e.g., first and/or second primerlayers) may vary over a range from about 0.1 microns to about 10microns. For instance, the thickness of the primer layer may be between0.1-1 microns thick, between 1-5 microns thick, or between 5-10 micronsthick. The thickness of a polymer layer may be no greater than, e.g., 10microns thick, no greater than 7 microns thick, no greater than 5microns thick, no greater than 3 microns thick, no greater than 2.5microns thick, no greater than 1 micron thick, no greater than 0.5microns thick, no greater than 0.3 microns thick, or no greater than 0.1microns thick. In some embodiments including a multi-layer primer, afirst primer layer has the same thickness as a second primer layer. Inother embodiments, the first primer layer may have a different thicknessthan the second primer layer.

In some cases, conductive fillers may be added to the material used toform a primer layer. Conductive fillers can increase the electricallyconductive properties of the polymeric material of the primer layer andmay include, for example, conductive carbons such as carbon black (e.g.,Vulcan XC72R carbon black, Printex Xe-2, or Akzo Nobel Ketjen EC-600JD), graphite fibers, graphite fibrils, graphite powder (e.g., Fluka#50870), activated carbon fibers, carbon fabrics, non-activated carbonnanofibers. Other non-limiting examples of conductive fillers includemetal coated glass particles, metal particles, metal fibers,nanoparticles, nanotubes, nanowires, metal flakes, metal powders, metalfibers, metal mesh. The amount of conductive filler in a primer layer,if present, may be present in the range of, for example, 10-90% or20-80% by weight of the primer layer (e.g., as measured after anappropriate amount of solvent has been removed from the primer layerand/or after the layer has been appropriately cured). For instance, thefirst and/or second primer layer may comprise a conductive filler in therange of 20-40% by weight, 20-60% by weight, 40-80% by weight, 60-80% byweight of the primer layer. In some embodiments, a conductive filler mayinclude a conductive polymer. Examples of suitable electroactiveconductive polymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. Preferred conductive polymers for certain embodimentsare polypyrroles, polyanilines, and polyacetylenes. Other conductivematerials known to those of ordinary skill in the art can also be usedas conductive fillers.

Mixing of the various components can be accomplished using any of avariety of methods known in the art so long as the desired dissolutionor dispersion of the components is obtained. Suitable methods of mixinginclude, but are not limited to, mechanical agitation, grinding,ultrasonication, ball milling, sand milling, and impingement milling.

Mixing of the various components can occur at various temperatures. Forinstance, the various components may be mixed at greater than or equalto 25° C., greater than or equal to 50° C., greater than or equal to 75°C., or greater than or equal to 90° C. for a suitable amount of time toobtain a desired dissolution or dispersion of components. For example,in some instances, a polymer used for a primer layer (e.g., polyvinylalcohol) is mixed at a temperature of greater than or equal to 25° C.,greater than or equal to 50° C., greater than or equal to 75° C., orgreater than or equal to 90° C. Mixing at such temperatures may beperformed until the polymer is dissolved and/or dispersed as desired.This solution/dispersion can then be mixed with other components of theprimer (e.g., a conductive filler, solvent, crosslinker, etc.), e.g., ata suitable temperature, to form a primer slurry.

The conductive support typically includes a conductive substance withgood adhesion and electrically conductive connection to the first primerlayer. The conductive support can function as a current collector usefulin efficiently collecting the electrical current generated throughoutthe electrode and in providing an efficient surface for attachment ofthe electrical contacts leading to the external circuit. A wide range ofconductive supports are known in the art. Suitable conductive supportsinclude, but are not limited to, those including metal foils (e.g.,aluminum foil), polymer films, metallized polymer films (e.g.,aluminized plastic films, such as aluminized polyester film),electrically conductive polymer films, polymer films having anelectrically conductive coating, electrically conductive polymer filmshaving an electrically conductive metal coating, and polymer filmshaving conductive particles dispersed therein. In some embodiments ofthe invention, the conductive support may comprise a conductive metalsuch as aluminum, copper, and nickel. Other conductive supports mayinclude, for example, expanded metals, metal mesh, metal grids, expandedmetal grids, metal wool, woven carbon fabric, woven carbon mesh,non-woven carbon mesh, and carbon felt.

Primer layers and electro active layers (e.g., cathode active layers)described herein may be deposited by any of a variety of methodsgenerally known in the art, and then dried using techniques known in theart. Suitable hand coating techniques include, but are not limited to,the use of a coating rod or gap coating bar. Suitable machine coatingmethods include, but are not limited to, the use of roller coating,gravure coating, slot extrusion coating, curtain coating, and beadcoating. Polymer layers can also be spin-coated onto a surface. Webcoating can also be employed. If removal of some or all of thesolvent/liquid from a mixture is desired, this can be accomplished byany of a variety of methods known in the art. Examples of suitablemethods for the removal of solvents from the mixture include, but arenot limited to, hot air convection, heat, infrared radiation, flowinggases, vacuum, reduced pressure, extraction, and by simply air drying.

Drying and/or crosslinking may be performed at a range of temperatures.Suitable temperatures include those above which the liquid mediumbecomes volatile, typically above the boiling point, and also those atwhich the crosslinking reaction between appropriate groups and thecrosslinking agent occurs at an acceptable rate. Suitable temperaturesare also below those at which the conductive support, for example, ametallized plastic film, may be deformed or damaged. In someembodiments, the drying and/or crosslinking step is performed at atemperature of from about 60-170° C.

In some embodiments, primer layers described herein can adhere to apositive or electroactive material, i.e., materials that form a cathode.Suitable electroactive materials for use as cathode active materials inthe cathode of the electrochemical cells of the invention include, butare not limited to, electroactive transition metal chalcogenides,electroactive conductive polymers, electroactive sulfur-containingmaterials, and combinations thereof. As used herein, the term“chalcogenides” pertains to compounds that contain one or more of theelements of oxygen, sulfur, and selenium. Examples of suitabletransition metal chalcogenides include, but are not limited to, theelectroactive oxides, sulfides, and selenides of transition metalsselected from the group consisting of Mn, V, Cr, Ti, Fe, Co, Ni, Cu, Y,Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Os, and Ir. In oneembodiment, the transition metal chalcogenide is selected from the groupconsisting of the electroactive oxides of nickel, manganese, cobalt, andvanadium, and the electroactive sulfides of iron. In one embodiment, acathode includes one or more of the following materials: manganesedioxide, carbon, iodine, silver chromate, silver oxide and vanadiumpentoxide, copper oxide, copper oxyphosphate, lead sulfide, coppersulfide, iron sulfide, lead bismuthate, bismuth trioxide, cobaltdioxide, copper chloride, manganese dioxide, and carbon. In anotherembodiment, the cathode active layer comprises an electroactiveconductive polymer. Examples of suitable electroactive conductivepolymers include, but are not limited to, electroactive andelectronically conductive polymers selected from the group consisting ofpolypyrroles, polyanilines, polyphenylenes, polythiophenes, andpolyacetylenes. Preferred conductive polymers include polypyrroles,polyanilines, and polyacetylenes.

In some embodiments, electroactive materials for use as cathode activematerials in electrochemical cells described herein includeelectroactive sulfur-containing materials. “Electroactivesulfur-containing materials,” as used herein, relates to cathode activematerials which comprise the element sulfur in any form, wherein theelectrochemical activity involves the oxidation or reduction of sulfuratoms or moieties. The nature of the electroactive sulfur-containingmaterials useful in the practice of this invention may vary widely, asknown in the art. For example, in one embodiment, the electroactivesulfur-containing material comprises elemental sulfur. In anotherembodiment, the electroactive sulfur-containing material comprises amixture of elemental sulfur and a sulfur-containing polymer. Thus,suitable electroactive sulfur-containing materials may include, but arenot limited to, elemental sulfur and organic materials comprising sulfuratoms and carbon atoms, which may or may not be polymeric. Suitableorganic materials include those further comprising heteroatoms,conductive polymer segments, composites, and conductive polymers.

Examples of sulfur-containing polymers include those described in: U.S.Pat. Nos. 5,601,947 and 5,690,702 to Skotheim et al.; U.S. Pat. Nos.5,529,860 and 6,117,590 to Skotheim et al.; U.S. Pat. No. 6,201,100issued Mar. 13, 2001, to Gorkovenko et al. of the common assignee, andPCT Publication No. WO 99/33130. Other suitable electroactivesulfur-containing materials comprising polysulfide linkages aredescribed in U.S. Pat. No. 5,441,831 to Skotheim et al.; U.S. Pat. No.4,664,991 to Perichaud et al., and in U.S. Pat. Nos. 5,723,230,5,783,330, 5,792,575 and 5,882,819 to Naoi et al. Still further examplesof electroactive sulfur-containing materials include those comprisingdisulfide groups as described, for example in, U.S. Pat. No. 4,739,018to Armand et al.; U.S. Pat. Nos. 4,833,048 and 4,917,974, both to DeJonghe et al.; U.S. Pat. Nos. 5,162,175 and 5,516,598, both to Visco etal.; and U.S. Pat. No. 5,324,599 to Oyama et al.

In one embodiment, an electroactive sulfur-containing material of acathode active layer comprises greater than 50% by weight of sulfur. Inanother embodiment, the electroactive sulfur-containing materialcomprises greater than 75% by weight of sulfur. In yet anotherembodiment, the electroactive sulfur-containing material comprisesgreater than 90% by weight of sulfur.

The cathode active layers of the present invention may comprise fromabout 20 to 100% by weight of electroactive cathode materials (e.g., asmeasured after an appropriate amount of solvent has been removed fromthe cathode active layer and/or after the layer has been appropriatelycured). In one embodiment, the amount of electroactive sulfur-containingmaterial in the cathode active layer is in the range of 5-30% by weightof the cathode active layer. In another embodiment, the amount ofelectroactive sulfur-containing material in the cathode active layer isin the range of 20% to 90% by weight of the cathode active layer.

Non-limiting examples of suitable liquid media (e.g., solvents) for thepreparation of cathodes (as well as primer layers of electrodesdescribed herein) include aqueous liquids, non-aqueous liquids, andmixtures thereof. In some embodiments, liquids such as, for example,water, methanol, ethanol, isopropanol, propanol, butanol,tetrahydrofuran, dimethoxyethane, acetone, toluene, xylene,acetonitrile, cyclohexane, and mixtures thereof can be used. Of course,other suitable solvents can also be used as needed.

Positive electrode layers may be prepared by methods known in the art.For example, one suitable method comprises the steps of: (a) dispersingor suspending in a liquid medium the electroactive sulfur-containingmaterial, as described herein; (b) optionally adding to the mixture ofstep (a) a conductive filler and/or binder; (c) mixing the compositionresulting from step (b) to disperse the electroactive sulfur-containingmaterial; (d) casting the composition resulting from step (c) onto asuitable substrate; and (e) removing some or all of the liquid from thecomposition resulting from step (d) to provide the cathode active layer.

Suitable negative electrode materials for anode active layers describedherein include, but are not limited to, lithium metal such as lithiumfoil and lithium deposited onto a conductive substrate, and lithiumalloys (e.g., lithium-aluminum alloys and lithium-tin alloys). Whilethese are preferred negative electrode materials, the current collectorsmay also be used with other cell chemistries.

Methods for depositing a negative electrode material (e.g., an alkalimetal anode such as lithium) onto a substrate may include methods suchas thermal evaporation, sputtering, jet vapor deposition, and laserablation. Alternatively, where the anode comprises a lithium foil, or alithium foil and a substrate, these can be laminated together by alamination process as known in the art to form an anode.

Positive and/or negative electrodes may optionally include one or morelayers that interact favorably with a suitable electrolyte, such asthose described in International Patent Application No.PCT/US2007/024805, filed Dec. 4, 2007 and entitled “Separation ofElectrolytes”, by Mikhaylik et al., which is incorporated herein byreference in its entirety.

The electrolytes used in electrochemical or battery cells can functionas a medium for the storage and transport of ions, and in the specialcase of solid electrolytes and gel electrolytes, these materials mayadditionally function as a separator between the anode and the cathode.Any liquid, solid, or gel material capable of storing and transportingions may be used, so long as the material is electrochemically andchemically unreactive with respect to the anode and the cathode, and thematerial facilitates the transport of ions (e.g., lithium ions) betweenthe anode and the cathode. The electrolyte may be electronicallynon-conductive to prevent short circuiting between the anode and thecathode.

The electrolyte can comprise one or more ionic electrolyte salts toprovide ionic conductivity and one or more liquid electrolyte solvents,gel polymer materials, or polymer materials. Suitable non-aqueouselectrolytes may include organic electrolytes comprising one or morematerials selected from the group consisting of liquid electrolytes, gelpolymer electrolytes, and solid polymer electrolytes. Examples ofnon-aqueous electrolytes for lithium batteries are described by Dornineyin Lithium Batteries, New Materials, Developments and Perspectives,Chapter 4, pp. 137-165, Elsevier, Amsterdam (1994). Examples of gelpolymer electrolytes and solid polymer electrolytes are described byAlamgir et al. in Lithium Batteries, New Materials, Developments andPerspectives, Chapter 3, pp. 93-136, Elsevier, Amsterdam (1994).Heterogeneous electrolyte compositions that can be used in batteriesdescribed herein are described in an U.S. Provisional application filedDec. 4, 2006 and entitled “Separation of Electrolytes”, by Mikhaylik etal.

Examples of useful non-aqueous liquid electrolyte solvents include, butare not limited to, non-aqueous organic solvents, such as, for example,N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates,sulfones, sulfites, sulfolanes, aliphatic ethers, cyclic ethers, glymes,polyethers, phosphate esters, siloxanes, dioxolanes,N-alkylpyrrolidones, substituted forms of the foregoing, and blendsthereof. Fluorinated derivatives of the foregoing are also useful asliquid electrolyte solvents.

In some cases, aqueous solvents can be used as electrolytes for lithiumcells. Aqueous solvents can include water, which can contain othercomponents such as ionic salts. As noted above, in some embodiments, theelectrolyte can include species such as lithium hydroxide, or otherspecies rendering the electrolyte basic, so as to reduce theconcentration of hydrogen ions in the electrolyte.

Liquid electrolyte solvents can also be useful as plasticizers for gelpolymer electrolytes, i.e., electrolytes comprising one or more polymersforming a semi-solid network. Examples of useful gel polymerelectrolytes include, but are not limited to, those comprising one ormore polymers selected from the group consisting of polyethylene oxides,polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides,polyphosphazenes, polyethers, sulfonated polyimides, perfluorinatedmembranes (NAFION resins), polydivinyl polyethylene glycols,polyethylene glycol diacrylates, polyethylene glycol dimethacrylates,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing,and optionally, one or more plasticizers. In some embodiments, a gelpolymer electrolyte comprises between 10-20%, 20-40%, between 60-70%,between 70-80%, between 80-90%, or between 90-95% of a heterogeneouselectrolyte by volume.

In some embodiments, one or more solid polymers can be used to form anelectrolyte. Examples of useful solid polymer electrolytes include, butare not limited to, those comprising one or more polymers selected fromthe group consisting of polyethers, polyethylene oxides, polypropyleneoxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes,derivatives of the foregoing, copolymers of the foregoing, crosslinkedand network structures of the foregoing, and blends of the foregoing.

In addition to electrolyte solvents, gelling agents, and polymers asknown in the art for forming electrolytes, the electrolyte may furthercomprise one or more ionic electrolyte salts, also as known in the art,to increase the ionic conductivity.

Examples of ionic electrolyte salts for use in the electrolytes of thepresent invention include, but are not limited to, LiSCN, LiBr, LiI,LiClO₄, LiAsF₆, LiSO₃CF₃, LiSO₃CH₃, LiBF₄, LiB(Ph)₄, LiPF₆,LiC(SO₂CF₃)₃, and LiN(SO₂CF₃)₂. Other electrolyte salts that may beuseful include lithium polysulfides (Li₂S_(x)), and lithium salts oforganic ionic polysulfides (LiS_(x)R)_(n), where x is an integer from 1to 20, n is an integer from 1 to 3, and R is an organic group, and thosedisclosed in U.S. Pat. No. 5,538,812 to Lee et al.

In some embodiments, electrochemical cells may further comprise aseparator interposed between the cathode and anode. The separator may bea solid non-conductive or insulative material which separates orinsulates the anode and the cathode from each other preventing shortcircuiting, and which permits the transport of ions between the anodeand the cathode.

The pores of the separator may be partially or substantially filled withelectrolyte. Separators may be supplied as porous free standing filmswhich are interleaved with the anodes and the cathodes during thefabrication of cells. Alternatively, the porous separator layer may beapplied directly to the surface of one of the electrodes, for example,as described in PCT Publication No. WO 99/33125 to Carlson et al. and inU.S. Pat. No. 5,194,341 to Bagley et al.

A variety of separator materials are known in the art. Examples ofsuitable solid porous separator materials include, but are not limitedto, polyolefins, such as, for example, polyethylenes and polypropylenes,glass fiber filter papers, and ceramic materials. Further examples ofseparators and separator materials suitable for use in this inventionare those comprising a microporous xerogel layer, for example, amicroporous pseudo-boehmite layer, which may be provided either as afree standing film or by a direct coating application on one of theelectrodes, as described in U.S. Pat. Nos. 6,153,337 and 6,306,545 byCarlson et al. of the common assignee. Solid electrolytes and gelelectrolytes may also function as a separator in addition to theirelectrolyte function.

The inventors have also discovered that lithium batteries having certainperformance characteristics can be achieved. For instance, in oneembodiment, a lithium battery including an anode comprising lithiummetal as the active anode species and a cathode comprising sulfur as theactive cathode species has an area specific resistance of less than 50ohm·cm². That is, the area specific resistance of the entire batteryassembly including any electrolyte, separator, or other component(s) ofthe battery is less than 50 ohm·cm². In certain embodiments, the areaspecific resistance of a lithium battery is less than 40, 30, 20, 10, or5 ohm·cm². Such area specific resistances can be achieved, in somecases, by using components that reduce the internal resistance orpolarization of the battery, and/or by promoting electronic conductionbetween components (e.g., between an electrode and a current collector).For example, in one embodiment, a lithium battery includes one or moreprimer layers positioned between the active cathode species and thecathode current collector, at least one of the primer layers including apolymeric material comprising hydroxyl groups. The primer layer(s) maycomprise or be essentially formed of polyvinyl alcohol, which may be atleast partially crosslinked or substantially uncrosslinked. The primerlayer(s) may have other characteristics (e.g., a certain weight percentcrosslinking) as described herein. The hydroxyl groups of the primerlayer may increase adhesion between the current collector and theelectroactive material and/or promote electrical conduction between theelectrode and the electroactive material, resulting in a lower areaspecific resistance of the battery. In addition, the inclusion of such aprimer layer in a battery may increase the discharge capacity andspecific energy density of the battery. For example, a battery includinga primer described herein may achieve an area specific resistance ofless than 50 ohm·cm² and an energy density of at least 150, 250, 350, or500 Wh/kg.

Those of ordinary skill in the art can determine area specificresistance by methods known in the art. For example, the area specificresistance of a particular battery can be determined as follows. Thebattery can be discharged and charged for a certain number of times. Atthe next cycle, fully-charged batteries can be discharged at differentcurrents (I), within a certain range. The cell voltage, V(I), can bemeasured at the middle of discharge at the different currents. Cellpolarization, P, can then be calculated as a difference between the cellopen circuit voltage (OCV) at the middle of discharge and the voltage ata certain current V(I) according to equation 1:P=OCV−V(I)  (1)The cell polarization vs. discharge current can be plotted; the slope ofthe line represents cell direct current resistance (DCR), as shown inequation 2.DCR=dP/dI  (2)

To determine cathode-separator-anode stack area specific resistance(ASR), the cell DCR can first be corrected for tab resistance R_(tab)(e.g., resistance of any tab used in the electrode assembly) and thenconverted into ASR by taking into account the active electrode area A,according to equation 3:ASR=(DCR−R _(tab))*A  (3)

Example 10 describes the fabrication of a lithium battery including aprimer layer comprising polyvinyl alcohol and the measurement of areaspecific resistance of the battery according to one embodiment of theinvention.

The figures that accompany this disclosure are schematic only, andillustrate a substantially flat battery arrangement. It is to beunderstood that any electrochemical cell arrangement can be constructed,employing the principles of the present invention, in any configuration.For example, with reference to FIG. 1, electrode 2 may be covered on theside opposite the side at which components 24, 26, and 30 areillustrated with a similar or identical set of components 24, 26, and30. In this arrangement, a substantially minor-image structure iscreated with a minor plane passing through electrode 2. This would bethe case, for example, in a “rolled” battery configuration in which alayer of electrode 2 is surrounded on each side by structures 24, 26,and 30 (or, in alternative arrangements layered structures illustratedin other figures herein). On the outside of each protective structure ofthe anode an electrolyte is provided and, opposite the electrolyte, anopposite electrode (e.g., an anode in the case of electrode 2 being acathode). In a rolled arrangement, or other arrangement includingmultiple layers of alternating anode and cathode functionality, thestructure involves anode, electrolyte, cathode, electrolyte, anode,etc., where each anode can include anode stabilization structures asdescribed in any part of this disclosure, or in more detail in U.S.patent application Ser. No. 11/400,025, filed Apr. 6, 2006, entitled,“Electrode Protection in both Aqueous and Non-Aqueous ElectrochemicalCells, including Rechargeable Lithium Batteries,” to Affinito et al.,which is incorporated herein by reference in its entirety. Of course, atthe outer boundaries of such an assembly, a “terminal” anode or cathodewill be present. Circuitry to interconnect such a layered or rolledstructure is well-known in the art.

The following examples are intended to illustrate certain embodiments ofthe present invention, but are not to be construed as limiting and donot exemplify the full scope of the invention. The following materialswere used as received in the Examples below: Celvol 425 (polyvinylalcohol) from Celanese Corporation; Celvol 165 (polyvinyl alcohol, 99.4%hydrolyzed) and Celvol 425 (polyvinyl alcohol, 96.0% hydrolyzed) fromCelanese Corporation; Vulcan XC72R (carbon black) from CabotCorporation; graphite (graphite powder), 50870, from Fluka; sulfur(elemental sulfur, sublimed, 100 mesh) from Alfa Aesar; Gel Tac 100G(acrylic adhesive) from Advanced Polymers International, Inc.; PrintexXE-2 (carbon black) from Degussa Corporation; Polycup 172 (a cationicamine polymer-epichlorohydrin adduct crosslinking agent) from Hercules;Dowanol PM (1-methoxy-2-propanol) from Dow Chemicals; PVP/VA 1-535(polyvinyl pyrrolidone vinyl acetate copolymer) from ISP; Butvar B98(polyvinyl butyral) from Solutia; Rhoplex GL 618 (acrylic binder) fromRhom and Haas; Ketjen EC-600 JD (carbon black) from Akzo Nobel;multifunctional aziridine from Bayer; ammonium hydroxide (29% solution),cat #22122-8, from Aldrich.

EXAMPLE 1

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode (including a2-micron-thick uncrosslinked polyvinyl alcohol first primer layer and analuminized polyethylene terephthalate (Al/PET) current collector),according to one embodiment of the invention. This example also showsthat the first primer layer achieved good adhesion to the currentcollector.

To prepare the primer, 6 wt % of polyvinyl alcohol (Celvol 425) and 94wt % of water were mixed at room temperature. The mixture was thenheated to 91 degrees Celsius under agitation until a clear solution wasachieved. A primer slurry was prepared by milling 5.4 wt % Vulcan XC72Rcarbon black, 34.6 wt % of isopropyl alcohol and 60 wt % of the Celvol425 solution in a ball mill with ceramic beads. The slurry was coated bya slot die onto both sides of a 6 micron thick aluminized polyethyleneterephthalate (Al/PET) film at a web speed of 12 feet/minute. Thecoating was dried in an oven at about 100 degrees Celsius. The driedprimer layer had a thickness of about 2 microns on each side of theAl/PET substrate. The thickness was measured using a Mitutoyo thicknessgauge (Japan). The substrate (Al/PET substrate) was measured before itwas coated, and then after it had been coated with the dried primer. Thethickness of the primer coating was measured as the difference betweenthe coated and uncoated substrate.

A cathode slurry was prepared by milling 83.22 wt % isopropyl alcohol,11.52 wt % sulfur, 3.52 wt % Printex XE-2 (carbon black), 0.32 wt %graphite, and 1.42 wt % Gel Tac 100G (acrylic adhesive) in an Attritorgrinder. This slurry was further diluted with water and isopropylalcohol to make a cathode slurry with 9 wt % solid containing 30 wt %water and 70 wt % isopropyl alcohol as co-solvents. The slurry wascoated with a doctor blade on top of the primer layer. The coatedcathode was dried at 80 degrees Celsius for three minutes and at 120degrees Celsius for three minutes. The coated cathode had 1.80 mg/cm² ofsulfur. The primer layer had good adhesion to both the substrate and thecathode composition.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch. 0.3 ml of electrolyte (86.4 wt% 1,3-dioxolane, 1 wt % lithium nitrate, and 12.6 wt % lithiumbis(trifluoromethylsulfonyl)imide) was injected into the pouch. Thepouch was sealed and the specific discharge capacities of the cell weremeasured, as shown in FIG. 4.

COMPARATIVE EXAMPLE 1

This comparative example describes a protocol for preparing anelectrochemical cell comprising a lithium anode and a sulfur cathodecomprising a standard Intelicoat primer for use as a comparison with theelectrochemical cell of Example 1. The sulfur cathode included a 6micron aluminized polyethylene terephthalate (PET) substrate with thetwo-layer Intelicoat primer: a first crosslinked primer layer (1.5microns thick) and a second uncrosslinked acrylate primer layer (1.5microns thick) applied to each side of the substrate.

The materials and procedures presented in Example 1 were used andfollowed, except a current collector with an Intelicoat primer(available from Intelicoat (formally Rexam Graphics), South Hadley,Mass.) was used instead of the polyvinyl alcohol primer to adhere thecathode to the aluminized polyethylene terephthalate current collector.The thickness of the Intelicoat current collector, including primerlayers on both sides of the substrate, was 12 microns.

The specific discharge capacities of the comparative example cell weremeasured (in mAh per gram of sulfur), as illustrated in FIG. 4. As shownin this figure, the electrochemical cell of Example 1 had a greaternumber of cycles having a specific discharge capacity greater than orequal to 800 mAh/gS than the electrochemical cell of ComparativeExample 1. Thus, it can be inferred that the uncrosslinked polyvinylalcohol first primer layer of Example 1 achieved good adhesion to boththe cathode and aluminized polyethylene terephthalate current collector,and has better stability in an electrochemical cell than the primer ofComparative Example 1.

EXAMPLE 2

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode (including a2-micron-thick uncrosslinked polyvinyl alcohol first primer layer and analuminum foil current collector), according to one embodiment of theinvention. This example also shows that the first primer layer achievedgood adhesion to the current collector.

To prepare the primer, 4.5 wt % of Celvol 165 (polyvinyl alcohol) and95.5 wt % of water were mixed at room temperature. The mixture was thenheated to 91 degrees Celsius under agitation until a clear solution wasachieved. A primer slurry was prepared by milling 4.2 wt % Vulcan XC72Rcarbon black, 27.88 wt % of isopropyl alcohol, 5.70 wt % of water, and62.22 wt % of the Celvol 165 solution in a ball mill with ceramic beads.The slurry was coated with a doctor blade onto one side of a 12 micronthick aluminum foil. The coating was dried in an oven at 85 degreesCelsius for 3 minutes and 120 degrees Celsius for 3 minutes. The driedprimer layer had a thickness of about 2 microns, as measured by thedifference between the thicknesses of the coated and uncoated substrate.

A cathode slurry was prepared by milling 83.22 wt % isopropyl alcohol,11.52 wt % sulfur, 3.52 wt % Printex XE-2 (carbon black), 0.32 wt %graphite, and 1.42 wt % Gel Tac 100G (acrylic adhesive) in an Attritorgrinder. This slurry was further diluted with water and isopropylalcohol to make a cathode slurry with 9 wt % solid containing 30 wt %water and 70 wt % isopropyl alcohol as co-solvents. The slurry wascoated with a doctor blade on top of the primer layer. The coatedcathode was dried at 80 degrees Celsius for three minutes and at 120degrees Celsius for three minutes. The coated cathode had 2.10 mg/cm² ofsulfur.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch. 0.3 ml of electrolyte (86.4 wt% 1,3-dioxolane, 1 wt % lithium nitrate, and 12.6 wt % lithiumbis(trifluoromethylsulfonyl)imide) was injected into the pouch. Thepouch was sealed and the specific discharge capacities of the cell weremeasured, as shown in FIG. 5.

COMPARATIVE EXAMPLE 2

This comparative example describes a protocol for preparing anelectrochemical cell comprising a lithium anode and a sulfur cathodecomprising a standard Intelicoat primer for use as a comparison with theelectrochemical cell of Example 2. The sulfur cathode included a 6micron aluminized polyethylene terephthalate (PET) current collectorwith a two-layer primer: a first crosslinked primer layer (1.5 micronsthick) and a second uncrosslinked acrylate primer layer (1.5 micronsthick) applied to each side of the current collector.

The materials and procedures presented in Example 2 were used andfollowed, except a 3 micron, two layer Intelicoat primer coating(available from Intelicoat (formally Rexam Graphics), South Hadley,Mass.) was used instead of the polyvinyl alcohol primer layer, and a 6micron aluminized PET film was used instead of a 12 micron thickaluminum foil as the current collector.

The specific discharge capacities of the comparative example cell weremeasured, as illustrated in FIG. 5. As shown in this figure, theelectrochemical cell of Example 2 had a longer cycle life than theelectrochemical cell of Comparative Example 2. Thus, it can be inferredthat the uncrosslinked polyvinyl alcohol single-layer primer of Example2 achieved good adhesion to both the cathode and aluminum foil currentcollector.

EXAMPLE 3

This example describes a protocol for preparing a prismaticelectrochemical cell comprising a lithium anode and a sulfur cathode(including a double layer primer comprising an uncrosslinked polyvinylalcohol layer and an uncrosslinked polyvinyl butyral/polyvinylpyrrolidone vinyl acetate copolymer layer, and an aluminum foil currentcollector), according to one embodiment of the invention. This examplealso shows that the double layer primer achieved good adhesion to boththe cathode and aluminum foil current collector.

To prepare the first primer layer comprising polyvinyl alcohol, 6.00 wt% of Celvol 425 (polyvinyl alcohol) and 94.00 wt % of water were mixedat room temperature. The mixture was then heated to 91 degrees Celsiusunder agitation until a clear solution was achieved. A first primerslurry was prepared by milling 33.30 wt % of isopropyl alcohol, 4.20 wt% of Vulcan XC72R carbon black, 2.00 wt % of Dowanol PM(1-methoxy-2-propanol), 25.50 wt % of water and 35.00 wt % of the Celvol425 solution in an Eiger mill with glass beads. The slurry was coatedwith a micro gravure coating head onto both sides of a 9 micron thickaluminum foil. The coatings were dried in an oven. The dried primerlayers had thicknesses of about 1.4 microns.

To prepare the second primer layer comprising polyvinylbutyral/polyvinyl pyrrolidone vinyl acetate copolymer, a second primerslurry was made by milling 76.90 wt % of isopropyl alcohol, 4.2 wt % ofVulcan XC72R carbon black, 9.80 wt % of Butvar B98 (polyvinyl butyral)solution (10 wt % solid in isopropyl alcohol) and 9.10 wt % of PVP/VA1-535 (polyvinyl pyrrolidone vinyl acetate copolymer) solution (20 wt %solid in IPA) in an Eiger mill with glass beads. The slurry was coatedwith a micro gravure coating head onto both sides of the first primerlayer. The dried second primer layers had thicknesses of about 0.6microns.

A cathode slurry was prepared by milling 88.00 wt % isopropyl alcohol,8.76 wt % sulfur, 0.60 polyethylene wax, 1.92 wt % Printex XE-2 (carbonblack), and 0.72 wt % Ketjen EC-600 JD carbon black in an Attritorgrinder. The slurry was coated with a die onto the second primer layerand dried in an oven. The coated cathode has a loading of 1.59 mg/cm² ofsulfur.

To fabricate an electrochemical cell, the cathode, a 9 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werewound together to form a prismatic cell, and placed in a pouch with 7.6grams of electrolyte (80.1 wt % 1,3-dioxolane, 12.3 wt % lithiumbis(trifluoromethylsulfonyl)imide, 1.0 wt % lithium nitrate, 6.6 wt % ofLi₂S₆). The pouch was sealed and the specific discharge capacities ofthe cell were measured, as shown in FIG. 6.

COMPARATIVE EXAMPLE 3

This comparative example describes a protocol for preparing a prismaticelectrochemical cell comprising a lithium anode and a sulfur cathode foruse as a comparison with the electrochemical cell of Example 3. Thesulfur cathode included a 12 micron aluminum foil substrate with atwo-layer primer: a first crosslinked primer layer (1.5 microns thick)and a second uncrosslinked acrylate primer layer (1.5 microns thick)applied to each side of the substrate.

The materials and procedures presented in Example 3 were used andfollowed to fabricate an electrochemical cell, except a 3 micron thicktwo layer Intelicoat primer (available from Intelicoat (formally RexamGraphics), South Hadley, Mass.) was used instead of the double layerprimer, and a 12 micron thick aluminum foil was used instead of a 9micron thick aluminum foil as the current collector.

The specific discharge capacities of the comparative example cell weremeasured, as illustrated in FIG. 6. As shown in this figure, theelectrochemical cell of Example 3 had a longer cycle life than theelectrochemical cell of Comparative Example 3. Thus, it can be inferredthat the double layer primer of Example 3 achieved good adhesion to boththe cathode and aluminum foil current collector.

EXAMPLE 4

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode (including a doublelayer primer comprising an uncrosslinked polyvinyl alcohol layer and anuncrosslinked polyvinyl pyrrolidone and polyvinyl acetate copolymerlayer, and an aluminum foil current collector), according to oneembodiment of the invention. This example also shows that the doublelayer primer achieved good adhesion to both the cathode and aluminumfoil current collector.

To prepare the first primer layer comprising polyvinyl alcohol, 6.00 wt% of Celvol 425 (polyvinyl alcohol) and 94.00 wt % of water were mixedat room temperature. The mixture was then heated to 91 degrees Celsiusunder agitation until a clear solution was achieved. A first primerslurry was prepared by milling 33.30 wt % of isopropyl alcohol, 4.20 wt% of Vulcan XC72R carbon black, 2.00 wt % of Dowanol PM(1-methoxy-2-propanol), 25.50 wt % of water and 35.00 wt % the Celvol425 solution in an Eiger mill with glass beads. The slurry was coatedwith a slot die coating head onto both sides of a 9 micron thickaluminum foil. The coating was dried in an oven. The dried primer layershad thicknesses of about 2.0 microns on each side of the substrate.

To prepare the second primer layer comprising uncrosslinked polyvinylpyrrolidone vinyl acetate copolymer and acrylic polymer, a second primerslurry was made by milling 8.8 grams of isopropyl alcohol, 8.4 grams ofwater, 0.4 grams of Dowanol PM (1-methoxy-2-propanol), 0.8 grams ofVulcan XC 72R (carbon black), 0.8 grams of PVP/VA 1-535 (polyvinylpyrrolidone vinyl acetate copolymer) and 0.8 grams of Rhoplex GL618 (anacrylic polymer binder) in a bottle with stainless steel balls. Theslurry was coated with a doctor blade onto the first primer layer. Thesecond primer layer was dried in an oven at 80 degrees Celsius for 3minutes. The thickness of the second primer layer was about 2 microns,as applied to each side of the substrate.

A cathode slurry was prepared by milling 88.00 wt % isopropyl alcohol,8.76 wt % sulfur, 0.60 polyethylene wax, 1.92 wt % Printex XE-d (carbonblack), and 0.72 wt % Ketjen EC-600 JD carbon black in an Attritorgrinder. The slurry was coated with a doctor blade onto the secondprimer layer. The cathode coating was dried in an oven at 80 degreesCelsius for 3 minutes and at 120 degrees Celsius for 3 minutes.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch. 0.3 ml of electrolyte (86.4 wt% 1,3-dioxolane, 1 wt % lithium nitrate, and 12.6 wt % lithiumbis(trifluoromethylsulfonyl)imide) was injected into the pouch. Thepouch was sealed and the specific discharge capacities of the cell weremeasured, as shown in FIG. 7.

EXAMPLE 5

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode including a double layerprimer comprising 1.) an uncrosslinked polyvinyl alcohol layer and 2.) acrosslinked layer including polyvinyl pyrrolidone/polyvinyl acetatecopolymer and acrylic polymer, wherein the ratio of the copolymer to theacrylic polymer was 2.1:1. The primer layers were deposited on analuminum foil current collector. This example shows that the doublelayer primer achieved good adhesion to both the cathode and aluminumfoil current collector. This example also illustrates that a secondprimer layer comprising a higher ratio of polyvinylpyrrolidone/polyvinyl acetate copolymer to acrylic polymer (e.g., aratio of 2.1:1 compared to 0.9:1 as described in Example 6) increasedadhesion between the second primer layer and the cathode.

To prepare the first primer layer comprising polyvinyl alcohol, theprocedure as described in Example 4 was followed.

To prepare the second primer layer comprising a crosslinked polyvinylpyrrolidone vinyl acetate copolymer and acrylic polymer, the procedureas described in Example 4 was followed to obtain the second primerslurry. The ratio of the polyvinyl pyrrolidone/vinyl acetate copolymer(PVP/VA 1-535) to acrylic polymer (Rhoplex GL 618) was 2.1:1. To 7 gramsof the second primer slurry was added 0.2 grams of Pfaz 322(multifunctional aziridine) solution (10% in isopropyl alcohol) and 1drop of ammonium hydroxide (29% water solution). The slurry was coatedwith a doctor blade onto the first primer layer. The second primer layerwas dried in an oven at 80 degrees Celsius for 3 minutes. The thicknessof the second primer layer was about 2 microns, as applied to each sideof the substrate.

To prepare the cathode coating layer, the cathode composition andprocedure described in Example 4 was followed.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch. 0.3 ml of electrolyte (86.4 wt% 1,3-dioxolane, 1 wt % lithium nitrate, and 12.6 wt % lithiumbis(trifluoromethylsulfonyl)imide) was injected into the pouch. Thepouch was sealed and the specific discharge capacities of the cell weremeasured, as shown in FIG. 7.

EXAMPLE 6

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode including a double layerprimer comprising 1.) an uncrosslinked polyvinyl alcohol layer and 2.) acrosslinked layer including polyvinyl pyrrolidone/polyvinyl acetatecopolymer and acrylic polymer, wherein the ratio of the copolymer to theacrylic polymer was 0.9:1. The primer layers were deposited on analuminum foil current collector. This example also shows that the doublelayer primer achieved good adhesion to both the cathode and aluminumfoil current collector.

To prepare the first primer layer comprising polyvinyl alcohol, theprocedure as described in Example 3 was followed.

To prepare the second primer layer comprising crosslinked polyvinylpyrrolidone/vinyl acetate copolymer and acrylic polymer, a second primerslurry premix was made by milling 8.6 grams of isopropyl alcohol, 8.6grams of water, 0.4 grams of Dowanol PM (1-methoxy-2-propanol), 0.8grams of Vulcan XC 72R (carbon black), 0.5 grams of PVP/VA 1-535(polyvinyl pyrrolidone-vinyl acetate copolymer) and 1.2 grams of RhoplexGL618 (an acrylic polymer binder) in a bottle with stainless steelballs. The ratio of the polyvinyl pyrrolidone/vinyl acetate copolymer(PVP/VA 1-535) to acrylic polymer (Rhoplex GL 618) was 0.9:1. The premixwas mixed with 0.2 grams of Pfaz 322 (multifunctional aziridine)solution (10 wt % in isopropyl alcohol) and 1 drop of ammonium hydroxide(29 wt % in water). The thickness of the second primer layer was about 2microns as applied to each side of the current collector.

To fabricate an electrochemical cell, the cathode, a 9 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werewound together to form a prismatic cell, and placed in a pouch with 7.6grams of electrolyte (80.1 wt % 1,3-dioxolane, 12.3 wt % lithiumbis(trifluoromethylsulfonyl)imide, 1.0 wt % lithium nitrate, 6.6 wt % ofLi₂S₆). The pouch was sealed and the specific discharge capacities ofthe cell were measured, as shown in FIG. 7.

COMPARATIVE EXAMPLE 4

This comparative example describes a protocol for preparing anelectrochemical cell comprising a lithium anode and a sulfur cathode foruse as a comparison with the electrochemical cells of Examples 4, 5, and6. The sulfur cathode included a 6 micron aluminized polyethyleneterephthalate (PET) current collector with a two-layer primer: a firstcrosslinked primer layer (1.5 microns thick) and a second uncrosslinkedacrylate primer layer (1.5 microns thick) applied to each side of thecurrent collector.

The materials and procedures presented in Example 3 were used andfollowed to fabricate an electrochemical cell, except a 3 micron thicktwo layer Intelicoat primer (available from Intelicoat (formally RexamGraphics), South Hadley, Mass.), coated on both sides of the currentcollector, was used instead of the double layer primer, and a 6 micronaluminized polyethylene terephthalate current collector was used insteadof a 9 micron thick aluminum foil current collector.

The specific discharge capacities of the comparative example cell weremeasured, as illustrated in FIG. 7. As shown in this figure, theelectrochemical cell of Example 5 had the highest specific dischargecapacities, followed by the cell of Example 6, and than the cell ofExample 4. These specific discharge capacities were higher than those ofthe electrochemical cell of Comparative Example 4. Thus, it can beinferred that the double primer layers of Examples 4, 5, and 6 achievedgood adhesion to both the cathode and aluminum foil current collector.This example also illustrates that the second primer layer of Example 5comprising a higher ratio of polyvinyl pyrrolidone/polyvinyl acetatecopolymer to acrylic polymer compared to that of Example 6, resulted inincreased adhesion between the second primer layer and the cathode.

EXAMPLE 7

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode including a2-micron-thick crosslinked polyvinyl alcohol single-layer primersupported by an aluminum foil current collector, according to oneembodiment of the invention. This example also shows that thesingle-layer primer achieved good adhesion to both the current collectorand cathode active material.

To prepare the crosslinked primer, 4.5 wt % of Celvol 165 (polyvinylalcohol) and 95.5 wt % of water were mixed at room temperature. Themixture was then heated to 90 degrees Celsius under agitation until aclear solution was achieved. A primer slurry was prepared by milling 4.2wt % Vulcan XC72R carbon black, 23.99 wt % of isopropyl alcohol, 5.70 wt% of water, and 62.22 wt % of the Celvol 165 solution in a ball millwith ceramic beads. A 2 wt % Polycup 172 solution (comprisingcrosslinking agent) was made by mixing 16.67 wt % of Polycup 172 and83.33 wt % of water. A final primer slurry was prepared by mixing theprimer slurry with the 2 wt % Polycup 172 solution before coating. Thefinal primer slurry was coated with a doctor blade onto one side of a 12micron thick aluminum foil. The coating was dried in the ovens of acoater. The dried primer layer had at thickness of about 2 microns.

A cathode slurry was prepared by milling 40.50 wt % water, 45.00 wt %isopropyl alcohol, 4.50 wt % of Dowanol PM (1-methoxy-2-propanol), 6.50wt % sulfur, 2.00 wt % Printex XE-2 (carbon black), and 1.50 wt %graphite in a glass bottle with stainless steal beads. The slurry wascoated with a die onto the above primer layer and dried in an oven ofthe coater. The coated cathode had 1.66 mg/cm² of sulfur.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch. 0.3 ml of TEK1 electrolyte(86.4 wt % 1,3-Dioxolane, 1 wt % lithium nitrate, and 12.6 wt % lithiumbis(trifluoromethylsulfonyl)imide) was injected into the pouch. Thepouch was sealed and the specific discharge capacities of the cell weremeasured, as shown in FIG. 8.

As shown in FIG. 8, the electrochemical cell of Example 7 had higherspecific discharge capacities than those of the electrochemical cell ofComparative Example 5 (which included a standard Intelicoat primer),especially after greater numbers of cycles. Thus, it can be inferredthat the uncrosslinked polyvinyl alcohol single-layer primer of Example7 achieved good adhesion to both the cathode active layer and thecurrent collector.

COMPARATIVE EXAMPLE 5

A small flat cell was fabricated and tested by the same procedure asdescribed in Example 8 except the cathode active material was coated onan Intelicoat primer on a 6 micron aluminized PET film.

EXAMPLE 8

This example describes a protocol for preparing an electrochemical cellcomprising a lithium anode and a sulfur cathode including a2-micron-thick crosslinked polyvinyl alcohol single-layer primersupported by an aluminum foil current collector, according to oneembodiment of the invention. This example also shows that thesingle-layer primer achieved good adhesion to both the current collectorand cathode active material.

To prepare the single-layer primer, 8 wt % of polyvinyl alcohol (Celvol425) and 92 wt % of water were mixed at room temperature. The mixturewas then heated to 91 degrees Celsius under agitation until a clearsolution was achieved. A primer slurry was prepared by mixing 31.33 wt %of isopropyl alcohol, 5.00 wt % of Dowanol PM (1-methoxy-2-propanol),20.20 wt % of water and 36.00 wt % the Celvol 425 solution (8.00 wt % inwater) in a container to form a Celvol 425 mixture. 4.8 wt % of VulcanXC72R carbon black was then added to the Celvol 425 mixture underagitation. This slurry was then milled in an Eiger mill for 40 minutes.The milled slurry was then mixed with 2.67 wt % of Polycup172 solution(comprising crosslinking agent) before coating. The slurry was coatedwith a slot die coating head onto both sides of a 7 micron thickaluminum foil. The coating was dried in an oven at about 100 degreesCelsius. The dried primer layer had a thickness of about 2.0 microns.The thickness was measured using a Mitutoyo thickness gauge (Japan). Thesubstrate (Al/PET substrate) was measured before it was coated, and thenafter it had been coated with the dried primer. The thickness of theprimer coating was measured as the difference between the coated anduncoated substrate.

A cathode slurry was prepared by milling 40.50 wt % water, 45.00 wt %isopropyl alcohol, 4.50 wt % of Dowanol PM (1-methoxy-2-propanol), 6.50wt % sulfur, 2.00 wt % Printex XE-2 (carbon black), and 1.50 wt %graphite in a glass bottle with stainless steal beads. The slurry wascoated with a die onto the above primer layer and dried in an oven ofthe coater. The coated cathode had 1.66 mg/cm² of sulfur.

To fabricate an electrochemical cell, the cathode, a 16 micron thickTonen film (used as a separator), and a 2 mil thick lithium foil werelaminated together and placed in a pouch (a small flat cell). 0.3 ml ofelectrolyte (86.4 wt % 1,3-dioxolane, 1 wt % lithium nitrate, and 12.6wt % lithium bis(trifluoromethylsulfonyl)imide) was injected into thepouch. The pouch was sealed tested.

The discharge capacity of the cells fabricated in Example 8 andComparative Example 6 are shown in FIG. 9. As shown in this figure, theelectrochemical cell of Example 8 had higher specific dischargecapacities than those of the electrochemical cell of Comparative Example6, especially after greater numbers of cycles. The electrochemical cellof Example 8 also had a longer cycle life than that of the cell ofComparative Example 6. Thus, it can be inferred that the uncrosslinkedpolyvinyl alcohol single-layer primer of Example 8 achieved goodadhesion to both the cathode active layer and the current collector.

COMPARATIVE EXAMPLE 6

This comparative example describes a protocol for preparing anelectrochemical cell comprising a lithium anode and a sulfur cathodeincluding a 2-micron-thick uncrosslinked polyvinyl alcohol single-layerprimer for use as a comparison with the electrochemical cell of Example8.

To prepare the uncrosslinked single-layer primer, 8 wt % of polyvinylalcohol (Celvol 425) and 92 wt % of water were mixed at roomtemperature. The mixture was then heated to 91 degrees Celsius underagitation until a clear solution was achieved. A primer slurry wasprepared by mixing 30.00 wt % of isopropyl alcohol, 5.00 wt % of DowanolPM (1-methoxy-2-propanol), 20.20 wt % of water and 40.00 wt % the Celvol425 solution (8.00 wt % in water) in a container to form a Celvol 425mixture. 4.8 wt % of Vulcan XC72R carbon black was then added to theCelvol 425 mixture under agitation. This slurry was then milled in anEiger mill for 40 minutes. The slurry was coated with a slot die coatinghead onto both sides of a 7 micron thick aluminum foil. The coating wasdried in an oven of the coater.

The dried primer layer had a thickness of about 2.0 microns. Thethickness was measured using a Mitutoyo thickness gauge (Japan). Thesubstrate (Al/PET substrate) was measured before it was coated, and thenafter it had been coated with the dried primer. The thickness of theprimer coating was measured as the difference between the coated anduncoated substrate.

The same cathode slurry as that of Example 8 was coated on the aboveprimer. The coated cathode had a loading of 1.60 mg/cm² of sulfur. Anelectrochemical cell was fabricated according to the procedure describedin Example 8.

EXAMPLE 9

This example describes the preparation and cycling of an electrochemicalcell comprising a lithium anode and a sulfur cathode including a2-micron-thick uncrosslinked polyvinyl alcohol single-layer primersupported by a 12-micron-thick aluminum foil current collector,according to one embodiment of the invention. This example shows that anelectrochemical cell made with the above-mentioned primer has betterperformance characteristics (e.g., higher discharge capacity andspecific energy density) than a cell made with a commercially-availableIntelicoat primer.

To prepare the primer, a slurry having a composition of 50 wt % VulcanXC72R (carbon black), 10 wt % graphite, and 40 wt % polyvinyl alcohol(Celvol 425) in a water/iso-propanol mixture was coated onto both sidesof a 12-micron-thick Al foil using a slot die. The coating was dried inan oven at about 100° C. The dried primer layers had a thickness ofabout 2 microns on each side of the Al foil. The primer layer had goodadhesion to the Al foil.

A cathode slurry was prepared by milling 68 wt % sulfur, 12 wt % PrintexXE-2 (carbon black), 10 wt % graphite, 5 wt % Ketjen black carbon, and 5wt % EAA (acrylic adhesive) in iso-propanol. The slurry was coated ontop of each of the primer layers. The coated cathode was dried at 110°C. The coated cathode had 1.57 mg/cm² of sulfur.

The anode electrode used was a 50-micron-thick Li foil.

The cathode and anode were wound together with a 9-micron-thickpolyolefin separator into a jellyroll. The area of the active electrodeswas 1141 cm². The cathode and anode tab contacts were attached to thejellyroll. The jellyrolls were placed into soft multi-layer packages,filled with 7.6 g of liquid electrolyte, and thermally sealed. Theelectrolyte had the following composition: 42.32 wt % of 1,3-dioxolane,42.32 wt % of 1,2-dimethoxyethane, 4 wt % of lithiumbis(trifluoromethylsulfonyl)imide, 3.77 wt % of lithium nitrate, 6.2 wt% of Li₂S₈, 1 wt % of guanidinium nitrate, and 0.4 wt % of pyridiniumnitrate.

Fresh electrochemical cells had an AC 1 kHz impedance 70 milliohms. Theprismatic cell mass was about 17.3 g. The cell was discharged at acurrent of 500 mA (C/5 rate) to a cutoff voltage 1.7 V. The celldischarge capacity at the C/5 rate was 2656 mAh. The specific energy atthe C/5 rate was 323 Wh/kg.

COMPARATIVE EXAMPLE 7

An electrochemical cell similar to the one described in Example 9 wasmade, with the exception that the 12 micron Al foil was coated on bothsides with an Intelicoat primer layer (available from Intelicoat(formally Rexam Graphics), South Hadley, Mass.) instead of the primerdescribed in Example 9.

Fresh electrochemical cells had an AC 1 kHz impedance of 160-200milliohms. The electrochemical cell was discharged at the sameconditions as those described in Example 9. The cell discharge capacityat the C/5 rate was 1868 mAh. The specific energy at the C/5 rate was218 Wh/kg.

EXAMPLE 10

This example describes the preparation and cycling of an electrochemicalcell comprising a lithium anode and a sulfur cathode including a2-micron-thick uncrosslinked polyvinyl alcohol single-layer primersupported by a 7-micron-thick aluminum foil current collector, accordingto one embodiment of the invention. This example shows that anelectrochemical cell made with the above-mentioned primer has betterperformance characteristics (e.g., lower area specific resistance anddirect current resistance) than a cell made with acommercially-available Intelicoat primer.

The primer layer described in Example 9 was coated on both sides of a7-micron-thick aluminum foil.

A cathode slurry was prepared by milling 73 wt % sulfur, 16 wt % PrintexXE-2 (carbon black), 6 wt % Ketjen black carbon, and 5 wt % polyethylenepowder in iso-propanol. The slurry was coated on top of each of theprimer layers. The coated cathode had a sulfur loading of 1.58 mg/cm².

The anode electrode used was a 50-micron-thick Li foil.

The cathode and anode were wound together with a 9-micron-thickpolyolefin separator into a jellyroll. The area of the active electrodeswas 1165 cm². Nickel cathode and anode tab contacts were attached to thejellyroll. The combined resistance of nickel cathode and anode tabcontacts (R_(tab)) was 15 milliohms. The cells were assembled and filledusing the same materials and methods described in Example 9.

The cell was discharged and charged four times. The discharge conditionswere as follows: 500 mA current, 1.7 V cutoff voltage. The chargeconditions were as follows: 315 mA current, 2.5 V cutoff voltage. At the5^(th) cycle, fully-charged cells were discharged at different currents,I, in the range from 0.5 A to 8.8 A. The cell voltage, V(I), wasmeasured at the middle of discharge at the different currents. Cellpolarization was calculated as a difference between the cell opencircuit voltage at this point and the voltage at a certain currentaccording to equation 1. Cell polarization vs. discharge current isplotted in FIG. 10. The slope of this plot (line 50) represents celldirect current resistance according to equation 2. The value of DCR was22.6 milliohms.

To determine cathode-separator-anode stack area specific resistance, thecell DCR was first corrected for tab resistance and then converted intoASR by taking into account the active electrode area A, according toequation 3. The value of ASR was 8.9 ohm·cm².

COMPARATIVE EXAMPLE 8

An electrochemical cell similar to the one described in Example 10 wasmade, with the exception that the 7-micron-thick aluminum foil currentcollector was coated on both sides with an Intelicoat primer layer(available from Intelicoat (formally Rexam Graphics), South Hadley,Mass.) instead of the primer described in Example 10.

The electrochemical cell was assembled electrical testing was performedusing the same method described in Example 10. The polarizationresistance of the Intelicoat-primer cells vs. discharge current isrepresented in line 52 of FIG. 10. The DCR represented by the slope ofthis plot had a value of 72.3 milliohms. The ASR of the cell was 66.8ohm·cm², which was calculated using Equation 3.

As shown in FIG. 10 and as described herein, the electrochemical cell ofExample 10 had a lower cell polarization as a function of currentdischarge (and, therefore, lower direct current resistance and areaspecific resistance) than the cell of Comparative Example 8. This showsthat the polyvinyl alcohol primer promoted better adhesion andelectrical conduction between the sulfur cathode and the Al foil currentcollector than the primer of Comparative Example 8.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of”, when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. An electrode comprising: a conductive support; aprimer layer comprising a polymeric material, wherein at least 10% byweight of the polymeric material is non-crosslinked, and wherein atleast a portion of the polymeric material is crosslinked; and anelectroactive layer in electrical communication with the primer layer,wherein the electroactive layer comprises an electroactivesulfur-containing material, wherein the primer layer adheres to theconductive support and the electroactive layer.
 2. An electrode as inclaim 1, wherein the polymeric material comprises hydroxyl functionalgroups.
 3. An electrode as in claim 1, wherein the polymeric material ispolyvinyl alcohol.
 4. An electrode as in claim 1, wherein the polymericmaterial is polyvinyl fluoride.
 5. An electrode as in claim 1, whereinthe electroactive layer is different from the primer layer.
 6. Anelectrode as in claim 1, wherein at least portions of the electroactivelayer and the primer layer are formed of different materials.
 7. Anelectrode as in claim 1, wherein at least a portion of the primer layerdoes not include an electroactive material.
 8. An electrode as in claim1, wherein the electroactive layer comprises a polymer includingfunction groups that can interact with functional groups of thepolymeric material of the primer layer.
 9. An electrode as in claim 1,wherein the primer layer is immediately adjacent the electroactivelayer.
 10. An electrode as in claim 1, wherein the primer layer includesa conductive filler in the range of 10-90% by weight of the primer layerafter the primer layer has been dried.
 11. An electrode as in claim 1,wherein the primer layer includes a conductive filler in the range of40-80% by weight of the primer layer after the primer layer has beendried.
 12. An electrode as in claim 10, wherein the conductive filler iscarbon black.
 13. An electrode as in claim 1, wherein the primer layerincludes a total amount of polymeric material in the range of 30-60% byweight of the primer layer.
 14. An electrode as in claim 1, wherein thethickness of the primer layer is less than 10 microns.
 15. An electrodeas in claim 1, wherein the thickness of the primer layer is less than 3microns.
 16. An electrode as in claim 1, wherein the primer layercomprises less than 30% by weight of a crosslinked polymeric material.17. An electrode as in claim 1, wherein the primer layer comprises lessthan 30% by weight of crosslinked polyvinyl alcohol.
 18. An electrode asin claim 1, wherein the electroactive sulfur-containing materialcomprises elemental sulfur.
 19. An electrode as in claim 1, wherein theelectroactive layer includes the electroactive sulfur-containingmaterial in the range of 20% to 90% by weight of the electroactivelayer.
 20. An electrode as in claim 1, wherein the polymeric material ofthe primer layer comprises hydroxyl functional groups and theelectroactive layer comprises a polymeric material comprising hydroxylfunctional groups.
 21. An electrode as in claim 20, wherein thepolymeric material comprising hydroxyl functional groups of the primerlayer is polyvinyl alcohol and the polymeric material comprisinghydroxyl functional groups of the electroactive layer is polyvinylalcohol.
 22. An electrode as in claim 21, wherein the primer layerincludes a conductive filler in the range of 10-90% by weight of theprimer layer after the primer layer has been dried.
 23. An electrode asin claim 1, wherein the primer layer includes greater than 10% by weightof crosslinked polymeric material.
 24. An electrode as in claim 1,wherein the primer layer includes greater than 30% by weight ofcrosslinked polymeric material.